This invention relates to photographic film cassette and camera systems employing same. More particularly, it concerns an improved cassette structure for retaining and handling a liquid impregated film component of a film system adapted for diffusion transfer processing.
Commonly assigned U.S. Pat. No. 3,907,563 issued to Edwin H. Land on Sept. 23, 1975 discloses a diffusion transfer process in which the image receiving element or sheet is impregnated with an alkaline processing composition. The image receiver or positive sheet includes a transparent support through which the final image may be observed in an image receiving coating or layer directly on the transparent support. Reflectivity for use of the sheet as a positive print is provided by a white pigmented layer backed by an opaque layer. The three layers thus provided on the transparent support are impregnated with a liquid alkaline processing agent common to diffusion transfer film processing.
The negative element of the system disclosed in the aforementioned patent includes a support of mylar or similar material which may be either transparent or opaque. The negative support is coated by polymeric acid layer, a timing layer, a dye developer layer and finally a silver halide layer. After exposure of the silver halide layer on the negative, the two sheets are brought together in intimate face-to-face contact as a laminate with the several coatings situated between the respective negative and positive sheet supports. The processing agent operates to transfer the latent image formed by exposure of the silver halide layer of the negative to the image-receiving layer directly behind the transparent support of the receiver sheet. The acid layer in the original negative sheet neutralizes the alkaline processing fluid but under the control of the timing interlayer situated between the acid layer and the remaining layers of the composite laminate.
The diffusion transfer system disclosed in U.S. Pat. No. 3,907,563 is especially attractive from the standpoint of attaining high quality photographs with virtually no provision for assuring uniformity of processing fluid spread between the respective negative and positive elements other than impregnation of the positive element during manufacture. In this respect, it is to be noted that in substantially all commercially available diffusion transfer film systems, the alkaline processing fluid is initially contained by a rupturable pod, carried as a component of the film assembly, to be spread between the negative and positive elements of the film assembly after negative exposure. The uniformity of this spread requires precision not only in the processing apparatus which is incorporated as a part of a camera or equivalent, but also a sophisticated and expensive combination of elements in the film sheet assembly, itself.
While a film system of the type disclosed in U.S. Pat. No. 3,907,563 has potential for significant reduction in costs over current diffusion transfer systems, particularly in the manufacture of film, use of such film on a commercial basis is not without problems. Because of the strongly alkaline character of the processing agent and the need for its neutralization after processing, the components carrying the processing agent and the neutralizing acid layer must be kept separate until the processing step is performed. Also, it is important that the liquid processing agent in the positive sheet element be kept from evaporization and that the pH level of the liquid be maintained. Moreover, these conditions must be maintained not only for the normal shelf life of commercial photographic film but also after the film is loaded into a camera and stored in the camera.
In two co-pending U.S. applications, Ser. No. 747,899 entitled "Wet Process Web Camera and Method" by the inventor, George D. Whiteside, now U.S. Pat. No. 4,630,912, and Ser. No. 747,901 entitled "Multi-Part Cassette for Two Component Film System" by the inventors, George D. Whiteside et at, now U.S. Pat. No. 4,630,915, on June 24, 1985, the aforementioned problems are addressed by the provision of a cassette system in which separate chambers are provided on opposite ends of a central tray-like section and to receive the respective negative and positive elements of the film system. The central tray-like section serves to retain the negative element of the system in an exposure plane and also, the positive chamber is equipped with a releasable stopper to ensure that the positive element, coated or otherwise wetted with a liquid processing agent, is hermetically encapsulated at all times other than during passage of the positive element from the chamber.
While the basic cassette organization disclosed in these co-pending applications shows great potential for commercial adaptation of the described two component film system, the problems associated particularly with assuring a sealed enclosure for the liquid impregnated or wet film component fall short of a total solution. For example, the requirement that a leading end portion of the wet film extend past the closed stopper not only involves a compromise of the sealing of the wet film component, but also results in evaporation of the liquid processing agent from the leading portion of the wet film projecting past the stopper. Also, contact with the wet film by the stopper gives rise to possible marking of the wet film and interferes with total sealing due to difficulties in making the pliant stopper seal about the edges of the film. In addition, structural components required to load and retain a coil of the wet film component in the stoppered enclosure was more complex and expensive than desirable for a one-use or disposable cassette structure. There is a need, therefore, for further improvement in the wet film enclosing and handling portion of the prior system. PG,6